As is generally known in the art, when a plurality of plastic members are stacked and fastened together as in materials used in the interior of vehicles, a riveting method is used in which a hole is defined through the plastic members adjacent to the edge of the plastic members, a rivet formed with a head on a first end thereof is inserted through the hole, and then a second end of the rivet is formed into the shape of a head.
In the case of materials used in the interior of vehicles, since the rivets are made of synthetic resin, differently from the case in which the rivets are made of a metallic material, a riveting operation is implemented in a manner such that synthetic resin is melted, one end of each rivet is formed into the shape of a head by applying pressure using a forming tool, and then the rivet is cooled.
In order to implement the riveting operation, a conventional riveting apparatus as shown in FIG. 1 has been disclosed in the art. In the conventional riveting apparatus, a heater 12 having an electric heating wire therein is coupled to the upper end of a forming tool 14 which functions to form an end of a rivet 1 into the shape of a head. If electric power is supplied, the heater 12 heats the forming tool 14 so that the temperature of the forming tool 14 is increased.
In the riveting apparatus, due to the fact that the forming tool 14 itself is heated, after the forming tool 14 is heated, the forming tool 14 is lowered such that the heating and the forming of the end of the rivet 1 can be simultaneously implemented.
The conventional riveting apparatus, which is constructed in such a way as to melt the end of the rivet 1 using the forming tool 14, provides the advantages of having a simple construction and being able to be fabricated at small cost. However, the conventional riveting apparatus suffers from drawbacks because, since the heating and the application of pressure are simultaneously implemented, pressure is likely to be applied when the end of the rivet 1 is not completely melted, and thereby, the end of the rivet 1 is likely to be inadequately formed into the shape of a head. Also, since the pressure can be transmitted to plate members 2, the plate members 2 are likely to be deformed or whitening can occur in the plate members 2, so that the quality of an end product deteriorates.
Further, because the temperature of the forming tool 14 slowly decreases upon cooling, it takes a long time to finish the riveting operation.
In another conventional riveting apparatus constructed as shown in FIG. 2(a), instead of directly heating a forming tool as described above, hot air is supplied around a rivet 1 to melt the rivet 1, and then a forming tool 24 is lowered to form an end of the rivet 1 into the shape of a head.
In this riveting apparatus, if plate members 2 and a rivet 1 reach a preset position, as shown in FIG. 2(b), a hot air supply unit 22 for supplying hot air is lowered to surround the end of the rivet 1 and then supplies hot air around the end of the rivet 1. Thereafter, after a predetermined time has elapsed, the hot air supply unit 22 is raised as shown in FIG. 2(c), and a punch, to which the forming tool 24 is coupled, is lowered to form the end of the rivet 1 into the shape of a head. Next, cooling air is supplied to cool the end of the rivet 1 which was formed into the shape of a head.
If hot air is used just as described above, since the forming tool 24 can be lowered to form the end of the rivet 1 after the end of the rivet 1 has sufficiently melted, the quality of the riveting operation can be improved upon when compared to the case of FIG. 1 in which the heating and the forming are simultaneously implemented.
Nevertheless, this conventional riveting apparatus has a drawback in that, since a driving unit for lowering and raising the hot air supply unit 22 and a driving unit for lowering and raising the forming tool 24 should be separately provided, the construction of the riveting apparatus becomes complicated and the fabrication cost of the riveting apparatus increases. Also, since the forming of the end of the rivet 1 is implemented by raising the hot air supply unit 22 after the end of the rivet 1 is heated by lowering the hot air supply unit 22, the time required to implement the riveting operation is extended.
Still another conventional riveting apparatus as shown in FIG. 3 has been developed by KIEFEL of Germany.
Referring to FIG. 3, in this conventional riveting apparatus, a heater 32 is coupled to the upper end of a forming tool 34, and the heater 32 and the forming tool 34 are surrounded by a housing. As air is supplied into the space defined in the housing, the air heated by the heater 32 is supplied toward an end of a rivet 1 to melt the end of the rivet 1, and then, the forming tool 34 is lowered to form the end of the rivet 1 into the shape of a head.
The conventional riveting apparatus provides an advantage in that, since it has a simple construction and can form the end of the rivet 1 into the shape of a head using hot air, the quality of a riveting operation can be elevated.
Nonetheless, the conventional riveting apparatus encounters a problem in that, because the size of the housing which surrounds the forming tool 34 and the heater 32 can not be increased beyond a certain size limit, the size of the heater 32 disposed in the housing is restricted and the amount of hot air for heating the end of the rivet 1 is limited, whereby a time required for melting the end of the rivet 1 can not but be extended. In particular, since hot air is supplied only to the outer surface of the end of the rivet 1, a lengthy period is required to melt the end of the rivet 1 up to the inside thereof. Further, when cooling the rivet 1, because the forming tool 34 and the heater 32 should also be cooled, the cooling time is lengthened. On the other hand, when heating the rivet 1, because the forming tool 34 and the heater 32 should be heated again, energy loss increases and it takes a long time to completely finish the riveting operation.